When one amp of current passes through a circuit with zero ohms (the unit of measure
for resistance) of resistance, no voltage drop occurs. Even when the circuit current
increases to 200 amps through zero ohms, still no voltage drop occurs. The amount
of resistance encountered by a current causes a voltage drop. Ohm's Law explains
how small resistance values can cause severe voltage drops. The basic form of
Ohm's Law is E = I x R, where the current, I in amps, is multiplied by the resistance,
R in ohms, to equal the voltage drop, E in volts. To see the affect resistance
has on voltage we use Ohm's Law and solve for voltage as shown here by the following
equation: I(Amps) X R(Ohms) = E(Voltage).

By substituting different values for resistance, we can see small resistances
can cause significant voltage drop problems, especially in high amperage systems
as shown below:

1 Amp X 0(Ohms)

=

0 (no voltage drop)

200 Amp X 0(Ohms)

=

0 (no voltage drop)

1 Amp X 1 Ohm

=

1.0 volt dropped

200 Amp X 0.01 Ohm

=

2.0 volt dropped

200 Amp X 0.02 Ohm

=

4.0 volt dropped

The Society of Automotive Engineers, S.A.E., has established the maximum voltage
drops for common electrical circuit cables and connections. The acceptable voltage
drops are shown below: